Add mutator for cacheMetadata config.
Add mutator for cacheMetadata config.

I need to modify this config option during test cases, and I don't want
to allow all the config options to be mutable.

jerems02/cakephp,bravo-kernel/cakephp,CakeDC/cakephp,nrother/cakephp,ndm2/cakephp,dkarvounaris/cakephp,jjj117/cakephp,thinkingmedia/cakephp,petteyg/cakephp,ionas/cakephp,ADmad/cakephp,gmponos/cakephp,eryw/cakephp,berrygoudswaard/cakephp,cakephp-fr/cakephp,pbaire/cakephp,timhoeppner/cakephp,ionas/cakephp,elboletaire/cakephp,dakota/cakephp,pbaire/cakephp,eboominathan/cakephp,khoimt/cakephp-study,davidyell/cakephp,eboominathan/cakephp,bravo-kernel/cakephp,CakeDC/cakephp,cakephp/cakephp,petteyg/cakephp,jeffblack360/cakephp,akintoey/cakephp,ionas/cakephp,CakeDC/cakephp,garethellis36/cakephp,mvdriel/cakephp,burriko/cakephp,tenkoma/cakephp,michaelze/cakephp,dakota/cakephp,tenkoma/cakephp,HavokInspiration/cakephp,tgr0ss/cakephp,elboletaire/cakephp,Phillaf/cakephp,davidyell/cakephp,jeffblack360/cakephp,elboletaire/cakephp,dkarvounaris/cakephp,cakephp/cakephp,tgr0ss/cakephp,erikfig/cakephp,thinkingmedia/cakephp,jjj117/cakephp,dkarvounaris/cakephp,web-player/cakephp,eryw/cakephp,khoimt/cakephp-study,kumamidori/cakephp,garethellis36/cakephp,davidyell/cakephp,tgr0ss/cakephp,burriko/cakephp,yinhe007/cakephp,tisu2tisu/cakephp,garethellis36/cakephp,erikfig/cakephp,dakota/cakephp,cakephp/cakephp,berrygoudswaard/cakephp,CVO-Technologies/cakephp,Balachan27/cakephp,petteyg/cakephp,Balachan27/cakephp,mvdriel/cakephp,adopico/cakephp,erikfig/cakephp,adopico/cakephp,michaelze/cakephp,garethellis36/cakephp,web-player/cakephp,pbaire/cakephp,dakota/cakephp,akintoey/cakephp,nrother/cakephp,kumamidori/cakephp,Phillaf/cakephp,ndm2/cakephp,petteyg/cakephp,jeffblack360/cakephp,cakephp/cakephp,Balachan27/cakephp,HavokInspiration/cakephp,web-player/cakephp,thinkingmedia/cakephp,gmponos/cakephp,ADmad/cakephp,ADmad/cakephp,cakephp-fr/cakephp,kumamidori/cakephp,nrother/cakephp,burriko/cakephp,gmponos/cakephp,ndm2/cakephp,tisu2tisu/cakephp,ndm2/cakephp,ADmad/cakephp,justinyost/cakephp,HavokInspiration/cakephp,yinhe007/cakephp,justinyost/cakephp,mvdriel/cakephp,adopico/cakephp,berrygoudswaard/cakephp,yinhe007/cakephp,michaelze/cakephp,tisu2tisu/cakephp,eryw/cakephp,akintoey/cakephp,jerems02/cakephp,CakeDC/cakephp,mvdriel/cakephp,justinyost/cakephp,tenkoma/cakephp,cakephp-fr/cakephp,timhoeppner/cakephp,khoimt/cakephp-study,CVO-Technologies/cakephp,bravo-kernel/cakephp,timhoeppner/cakephp,jerems02/cakephp,eboominathan/cakephp,jjj117/cakephp,tenkoma/cakephp,Phillaf/cakephp,CVO-Technologies/cakephp